The present invention relates to an eyeglass lens processing apparatus for processing a periphery of an eyeglass lens.
In eyeglass lens processing apparatuses used by an optician, a mainly used apparatus is that in which while an eyeglass lens held by a lens chuck shaft is rotated, an axis-to-axis distance between a grindstone spindle attached with roughing grindstone and the lens chuck shaft is changed based on target lens shape data, and the periphery of the lens is roughened by the roughing grindstone. In roughing a plastic lens by the roughing grindstone, a down-cut system in which a rotating direction of roughing grindstone 166 and that of an eyeglass lens LE are set opposite to each other, as shown in FIG. 1A, is adopted. The reason for this is that when an up-cut system in which the rotating direction of the roughing grindstone 166 and that of the lens LE are the same is adopted, as shown in FIG. 1B, if the lens LE is deeply cut by the roughing grindstone 166, a force for pulling the lens LE to a grindstone side is increased, as indicated by an arrow FB, and thus, a so-called axial deviation, in which an axial angle of the lens LE is deviated relative to a rotating angle of the lens chuck shaft, is greatly generated. On the other hand, in the down-cut system, even when the lens LE is deeply cut by the roughing grindstone 166, the force for pulling the lens LE to the grindstone 166 side, as indicated by an arrow FA, does not act (or weak), and thus, the generation of the axial deviation is small.
In the down-cut system, the generation of the axial deviation is small. However, recently, there is a water-repellent lens of which the lens surface is coated with a water-repellent substance to which water, or oil, etc., does not easily adhere. At the time of processing the water-repellent lens, axial deviation tends to occur. As a method for alleviating the axial deviation, there has been proposed a technique in which a rotation torque of a lens chuck shaft for holding a lens is detected and a lens rotation speed is decelerated so that the rotation torque does not exceed a predetermined value, or an axis-to-axis distance between the lens chuck shaft and a grindstone spindle is moved in a direction into which the distance is enlarged (JP-A-2004-25561 (US 2004-0192170)). As another method, there has been proposed a technique in which a lens is rotated at a constant speed, and an axis-to-axis distance between a lens chuck shaft and a grindstone spindle is varied so that a cutting amount while the lens makes one rotation is substantially constant (JP-A-2006-334701).
However, in the down-cut system, there is a problem in that a processing sound is larger at the time of roughing as compared to the up-cut method. To suppress the generation of the large processing sound in the down-cut system, some measures there have been introduced. However, there is no example in which the effect is actually provided. When the up-cut system is adopted, the problem of the aforementioned axial deviation is present even in a normal lens, and in the water-repellent lens, the problem of the axial deviation becomes even more conspicuous.
As a method for alleviating the axial deviation in the water-repellent lens, the technique of JP-A-2004-25561 (US 2004-0192170) was adopted in the down-cut system. As a result, due to advancement of the roughing, a case where the rotation torque is applied to a plus side opposite to the rotating direction of the lens and a case where the rotation torque is applied to a minus side which is the same direction as the rotating direction of the lens frequently occur. Thus, controlling of a change of the axis-to-axis distance or the lens rotation speed is difficult, and therefore, its application is difficult. Further, when the cutting amount increases, a permissible value of the torque applied to the lens is rapidly exceeded, and when it is controlled so that the lens is rapidly kept apart from the grindstone so as to decrease the torque, the lens chuck shaft is vibrated in up and down directions.
On the other hand, at the time of adopting the technique of JP-A-2006-334701 in the down-cut system, when a lens thickness is unknown, there is a need for estimating the thickest lens and setting the cutting amount to very small amount for the sake of safety so that no axial deviation is generated. In this case, the number of rotations of the lens is increased, and thus, the processing time is lengthened. Even when the lens thickness is measured, accurate measurement of the lens thickness is not easy, and in an astigmatic lens, the lens thickness differs depending on each radial angle, and thus, it is even more difficult to know the lens thickness over the entire lens.